Printing device



May 24, 1960 w. WOCKENFUSS PRINTING DEVICE 2 Sheets-Sheet 2 Filed NOV. 12, 1957 INVENTOR. ML LMM n OOKE NF U88 ATTORNEY United States Patent PRINTING DEVICE William Wockenfuss, Brooklyn, N.Y., assignor to Burroughs Corporation, Detroit, Mich., a corporation of Michigan Filed Nov. 12, 1957, Ser. No. 695,686

12 Claims. (Cl. 101-91) This invention relates generally to a printing device and more particularly to a device that can print a character through a multiple number of carbon copies with a minimum degree of character divergence.

Present day business procedures often require multiple carbon copies. Unfortunately, however, as we have all experienced, the readability of carbon copies decreases as the number of carbon copies made simultaneously is increased. This condition is caused by the progressive blurring or divergence of the characters as they are transferred through each next appearing sheet of a stack to limit the number of acceptable carbon copies that can be printed simultaneously. In many instances the required information must be originally presented two or more times to obtain the required number of readable copies. This procedure is time consuming and costly.

It is a primary object of this invention to provide an improved printing device that can-print a character on a plurality of carbon copies simultaneously with a minimum of character divergence.

It is another object of this invention to provide an improved printing device that is economical to produce and reliable in operation.

A feature of this invention is found in its adaptability to print selectively on opposite sides of a sheet or sheets of paper simultaneously.

Other objects, features and many of the attendant advantages of this invention will be readily appreciated as the apparatus becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:

Fig. l is a view illustrating the divergence of a character through a stack of paper backed by an infinite platen;

Fig. 2 is a view illustrating the decreased divergence of a character through the same stack of paper in accordance with the principles of this invention;

Fig. 3 is a side view of a printing device in accordance with the principles of this invention;

Fig. 4 is an enlarged view of the printing members; and

Fig. 5 is a block diagram of the character indexing device.

- Similar reference characters refer to similar parts throughout the several views of the drawings.

Briefly, the required number of sheets that are to receive the required impressions arte stacked flat one on top of another and interleaved with carbon paper in the usual manner. A first type face is positioned adjacent to one side of the stack, and a second type face-the mirror image of the first type face-4s positioned adjacent to the other side of the stack and aligned with the first type face. At an appropriate instant the two aligned mirror image type faces are first driven together, relative to each other, to compress the stack; and then withdrawn to their initial position. By utilizing mirror image or matched type faces to print a character through a number of carbon copies simultaneously the maximum divergence of the printed character is reduced to a minimum to permit the simultaneous printing of an increased number of'acceptable copies.

The principle of operation of this invention, and its advance over the old single type face and infinite platen The dotted lines indicate the progressive divergence of the character from the topmost sheet of the stack to the bot-. tom sheet.

For a stack of sheets of T thickness, the maximum divergence of a character will be a distance represented by the numeral 28 and occurs on the sheet positioned furthest from the type face.

With reference to Fig. 2, however, which illustrates the principle of this invention, a type face 30 mounted on a block 32 is positioned adjacent to a top sheet of a stack of papers 34 of T thickness interleaved with carbon paper in the usual manner. A second block 38 supports a type face 36 that is a mirror image of the type face 30. The type face 36 is positioned adjacent to the bottom sheet of the stack and aligned with the type face 30. To print a character on each sheet of the stack simultaneously the blocks 32 and 38 are driven together relative to each other to compress the stack 34between the mirror image type faces 30 and 36. The dotted lines 31 indicate the divergence of the character through the stack from the top sheet to the bottom sheet. The maximum divergence of this character occurs at the center of the stack and is indicated by the numeral 39'.

A comparison of Figs. 1 and 2 readily illustrate the ad;

vantage of this invention in reducing the maximum divergence of a character printed through a stack of papers. With reference to Fig. 3, there is illustrated a side'view of structure in accordance withthe principles of thisinf vention for impressing a character on each sheet of a The stack is positioned face down in a support and guide member 42 that contains a stationary top backing plate 43 and movable bottom plate 45. The bottom plate 45 is urged upward towards the top backing plate by springs to provide a fixed position for the topmost sheet of they stack regardless of its thickness. Each plate 43 and 45 contains a cutout portion to expose opposite sidesof the stack for the receipt of a character impression. Two feed rollers 44 and 46 rotatably supported by the shafts 48 and 50 respectively support one end of the stack 40. A

stack stepping assemblage 51, coupled to the other end of the stack, selectively steps the stack of paper in the direction indicated by the arrow. The stepping assemblage 51 consists of a shaft 60 that rotatably supports an arm 58, a ratchet wheel 63 and a drum 64. The drum 64- is rigidly connected to the ratchet wheel 63 by pins,

solder or the equivalent. The arm 58 is pivotally con nected to a pawl '62 through a pin 61, and to a plunger 54 of a solenoid 52 through a pin 56. A spring urges the pawl into engagement with the ratchet wheel 63. A plurality of outwardly projecting retractable pins 66 extends radially from each end of the drum '64 and engages circular cutouts positioned adjacent to the side edges of the stack of paper 40 to insure aligned positive movement of each sheet in the stack. An idler roller 68 positioned beneath the drum 64 is rotatably supported on a shaft 70. A spring coupled to the shaft 70 urges the roller into the bottom of the stack to maintain the stack of paper in contact with the drum 64. The pins 66, when in their extended position, are slightly longer than the maximum thickness of the stack. To insure movement of the lowermost sheet and prevent interference between the pins 66 and the roller 68 during the stepping of the stack, the roller is provided with clearance channels adjacent to each end and aligned to accept the projecting pins. The clearance channel should be deep enough to accommodate the pins when a character is being printed on only one or two sheets as well as when a character is being printed on the maximum number of sheets.

v Normally, the solenoid is not energized and the plunger 54 is withdrawn into the solenoid by a spring. To advance the stack of paper one line position the solenoid 52 is energized by a single potential pulse to urge the plunger 54 out of the solenoid 52 against the action of the spring to drive the drum 64 and therefore the pins 66 in a counterclockwise direction through the action of the pawl 62 and the ratchet wheel 63. The cooperation of the pins 66 with the circular cutouts in the stack of paper uniformly advance each sheet in the stack one line position. After the stack has been stepped the potential pulse is removed from the solenoid and the plunger is urged to its withdrawn position. The return stroke of the plunger rotates the arm 58 and pawl 62 in a clockwise direction to position the pawl to a new position on the ratchet wheel 63 in preparation for the next stepping cycle. Thus, each instant that the solenoid 52 is energized and the plunger 54 is advanced, the stack of papers advances one line position through the action of the rotatable arm 58, the pawl 62, and the ratchet wheel 63.

Positioned immediately below and adjacent to the stack of paper 40 is a wheel 72 rotatably connected to an end 74 of a rocker arm 76 by means of a shaft 78. Type face 80, one for each distinctive character required for presentation, is secured rigidly to the periphery of the wheel 72 by solder or the equivalent. The rocker arm 76 is pivotally coupled to oscillate about a shaft 82.

Positioned immediately above and adjacent to the stack of paper 40 is a second wheel 84 rotatably connected to rotate about a fixed shaft 86. Type face 88, one for each distinctive character required for presentation is secured rigidly to the periphery of the wheel 84 by solder or the equivalent.

The two wheels 72 and 84 support the same number of type faces, however, for each particular type face on wheel 72, its mirror image type face is present on wheel 84. With reference to Fig. 4, there is shown an enlarged view of a portion of the periphery of the two wheels 72 and 84. The type face 80 on the wheel 72 acts as the printing type face and is aligned with a type face 88 on the wheel 84. The type face 88 acts as a platen for and is a mirror image of the type face 80. It should be noted that the type faces are oriented to present impressions on the under side of each sheet of the stack. For purposes of convenience the wheel 72, since it supports the printing type faces shall hereafter be referred to as the print wheel; and the wheel 84, since it supports the platen type faces shallhereafter be referred to as the platen wheel.

Referring again to Fig. 3, the order of sequence and spacing of the type faces on the platen wheel are the same as the order of sequence and spacing of the type faces on the print wheel to enable the two type faces required to form each character to be presented simultaneously to opposite sides of the stack. Thus, each instant that the print wheel presents a type face to the bottommost sheet of the stack, the platen wheel presents a mirror image type face of the print wheel type face to the topmost sheet of the stack. The positions of the type faces 88 are fixed relative to. the top of the stack by the action of the sta- 4 tionary top backing plate 43 and the fixed shaft 86 of the wheel 84.

During the printing operation the print wheel and platen wheel must present type faces that are mirror images of each other simultaneously to opposite sides of the stack. In operation the two wheels are rotated continuously, therefore, to secure synchronized displacement of the two wheels relative to each, other a set of coupling gears are utilized. A gear train consisting of the interconnecting gears 90, 92, 94 and 96 couple the print wheel to the platen wheel. The gear train functions as a synchronizing means to insure accurate alignment of the mirror image or matched type faces on the print and platen wheels at all times. The gear is rotatably supported by the shaft 82 and is driven by a gear 98 which is driven by an electric motor.

Since the two wheels are continuously driven at a constant speed, the printing process must be performed while the wheels are in motion. This process is known as printing on the fly and is accomplished by driving the matched type faces together and apart rapidly relative to each other to alternately compress and release the stack between the type faces at the instant that the matched type faces of the desired character are positioned on opposite sides of the stack. This is accomplished by oscillating the rocker arm 76 about its shaft 82 to compress and release the stack between the non-yielding type face 88 and the vertically driven type face 80. The linear motion of the rocker arm is very fast relative to the rotary motion of the print and platen wheels and eifectively stops the rotation of the wheels to produce a clear smudge free impression.

The rocker arm 76 and gear 90, while rotatably sup ported by the same shaft 82, rotate independently of each other. The lower end 100 of the rocker arm 76 is pivotally connected to one end of a push link 102 through a shaft 104. The other end of the push link is connected to a spring 103 which urges the push link to rotate clock.- wise about the shaft 104. The lower edge of the push link is cutout to present a wedge shaped tooth 106. Positioned beneath the push link 102 is a fluted drive 108 and a fluted drive bear 110 coupled to each other by solder, rivets or the equivalent and rotatably supported by a shaft 112. A gear 114 connects the drive gear 98 to the fluted drive gear 110.

The fluted drive is driven continuously in a clockwise direction. The spring 103 urges the push link 102 upward to prevent the fluted drive 108 from contacting the tooth 106. A latch member 116 is pivotally connected to the push link 102 by a shaft 118. The latch member is maintained captive by a slotted cutout 120 which cooperates with a stationary guide pin 122. The lower end of the latch member supports a horizontal projection 124 which cooperates with the free end of a pivoted arm 126. The arm 126, its magnetic path U shaped structure 127, and a coil of wire 128 make up an electromagnet assemblage.

At the instant that it is desired to print a character on each sheet of the stack, the coil 128 is energized and the arm 126 is urged downward. The latch member 116 follows the arm 126 and, against the action of the spring 103, positions the tooth 106 of the push link 102 downward within the path of travel of a projection 111 on the rotating fluted drive 108. An instant later the projection 111 strikes the tooth 106 to urge the rocker arm 76 to rotate in a counterclockwise direction about the shaft 82. The rotation of the rocker arm drives the print wheel 72 into the bottom sheet of the stack and, since the non-yieldable platen wheel is in synchronism with the print wheel, the platen wheel presents a mirror image type face to the top sheet of the stack. Immediately after the print wheel contacts the stack of paper 40 the coil 128 is deactivated, and the spring 103 urges the push link 102 and the tooth 106 upward free of the path of travel of the projections on a fluted drive 5. 108. At the same, time a projection on a second fluted drive 130, driven in synchronism with the fluted drive 108, strikes a small projection 132on the end 100 of the rocker arm 76' to drive the print wheel away from the stack by driving the rockerarm in a clockwise direction In the embodiment disclosed in Fig. 3, if the print wheel and platen wheel each support forty distinctive characters; then accurate timing of the printing cycle will be assured if the fiuated drive 108 supports eight projections and is driven at a'rotational speed five times the rotational speed of the print and platen wheels; and the return drive 130 supports two projections and is driven at a rotational speed four times greater than the rotational speed of the fluted drive 108.

It should be understood that these values are given for illustrative purposes only, the actual ratios of speeds being dependent upon the number of distinctive characters that are to be presented, and on the number of projections desired on the fluted drive 108 and the return fluted drive 130. It must be remembered, however, that since the printing is performed while the print and platen wheels are rotating, that the print wheel must be cycled rapidly relative to its rotational speed.

In operation, a stack of sheets 40 are positioned within the support and guide member 42 which exposes opposite sides of a portion of the stack to the print wheel 72 and the platen wheel 84, and threaded to the stack stepping assemblage 51. The coil 128 is not energized, the tooth 106 is positioned above the fluted drive 108, and the driver gear 98 drives the print wheel 72, the platen wheel 84, the fluted drive 108 and the return drive 130 continuously through idler gears at predetermined speeds relative to each other. Initially, the tooth 106 of the push link 102 is in its extreme left hand position and urged upward away from the continuously rotated fluted drive 108 by the spring 103. Immediately prior to the presentation of desiredmatched or mirror image type faces to each side of the stack by the platen and print wheels, the coil 128 is energized, the pivoted arm 126, acting through the latch member 116 urges the push link down against the action of the spring 103 to position the tooth 106 in the path of the next arriving projection 111 on the fluted drive 108. The moving projection 111 strikes the tooth 106 to impell the push link 102 rapidly towards the right to drive the rocker arm 76 in a counterclockwise direction. This movement of the rocker arm drives the print wheel upward to impress the desired type face into the bottommost sheet of the stack. The stack is driven up very slightly to contact the non-yielding match type face on the platen wheel 84. In this manner the stack is compressed by mirror image type faces to impress a character on each sheet of the stack with a minimum of divergence. Immediately after the desired type face on the print wheel contacts and impresses the desired character on each sheet of the stack simultaneously, the coil 128 is deenergized, the push link 102 is urged-upward free of the fluted drive 108 by the spring 103, and the return drive 130 strikes the projection 132 to drive the rocker arm 76 clockwise about the shaft 82 to withdraw the print wheel from contact with the stack. The push link 102 is now in position for the printing of a next appearing character.

When the character impressions are recorded on tape the stack stepping assemblage 51 is activated a predetermined number of times immediately after each character is printed to step the tape to the proper position. For example, the assemblage 51 is activated to advance the stack one print position between letters of each word, two print positions between words in the same sentence, and three print positions between sentences.

Detection of the exact displacement of the print and platen wheels from a reference position to locate a de sired character can be accomplished by a number of methods one in Fig. 5.

j A permanent magnet 134 positioned to rotate aboutiflie t pole represents a distinctive type face and the spacing between adjacent poles is equal to the spacing between adjacent type faces. A separate coil of wire 138 is wound around each projecting pole 136 and generates a potential pulse each instant that the magnet 134 induces a magnetic field in an associated pole 136. One end of each coil of wire is connected to a ground terminal, and the other end is connected to an input terminal of an AND gate 140. A source of potential is fed through an on-oif switch 142 to a second input terminal of the AND gate.

The AND gate passes a potential pulse only when a signal is present on each of the two input terminals simultaneously. A signal will not appear on the output terminal of an AND gate if a signal is absent from either one or both of the input terminals. There is one AND gate 140 for each pole 136 and coil 138; and one pole 138 for each distinctive type face supported by the platen wheel 84. The output terminals of the AND gates are coupled to feed a signal through the coil 128.

In operation, the permanent magnet 134 is rigidly coupled to and therefore rotates at the same speed as the platen wheel 84. The inwardly projecting poles are locked in a fixed, non-movable position. Each instant that the permanent magnet 134 moves past a pole 136, a potential pulse is generated within the associated coil of wire 138. It is now possible to identify a type face that is adjacent to the stack of paper by merely identifying a coil of wire 138 that exhibits a potential pulse since the orientation of the permanent magnet 134 relativeltothe type faces on the wheel is known, and the order of occurrence of the typefaces is also known. The actual, generation of a pulse signal to indicate the presence of a desired type face in the print position is accomplished by means of the AND gates. To print the letter A on a stack of sheets, the switch 142 associated with the letter A is closed by automatic or manual means to feed a potential signal to the AND gate associated with the. coil 138 that is representative of the letter A. Immediately before the type faces for the letter A appear on each side of the stack, the. coil 138 that represents the letter A will generate a potential through the action of the rotating permanent magnet 134. This potential signal is fed through the activated gate 140 to energize the coil 128 to initiate the printing process.

In some applications of this invention it may be desirable to print information on a sheet rather than on a strip of paper. This can be accomplished by stacking a number of platen Wheels adjacent to each other to rotate about a common axis; and by stacking an equal number of print wheels adjacent to each other; each print wheel being in alignment with a platen wheel. The print and platen wheels can be locked together to rotate at the same speed, however, the print wheels must be individually supported for separate activation. In this embodiment the sheet of paper will be stepped to receive a newline of information, it will not he stepped to separate letters, words or sentences. The spacing between the wheels determines the spacing between adjacent characters, and words and sentences can be separated by selectively inactivating particular print wheels. a

In the embodiment described above for printing a line of characters on a sheet of paper, it was assumed that all of the platen wheels were positioned adjacent to one side of the stack, and that all of the print wheels were positioned adjacent to the other side of the stack. This arrangement presents printed characters on one side of each sheet of paper. If, however, the platen and print wheels of which is the indexing means illustrated are divided into two matched groups; and the platen wheels of one of the groups are interchanged with their matched print wheels, then this device can print selectively on opposite sides of each sheet of paper simultaneously. Naturally care must be exercised to prevent backward printing of the information that would appear on the reverse side of the sheet.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed is:

l. A device for printing a character on a plurality of sheets of paper interleaved with pressure sensitive marking means to form a stack comprising a first rotatable support member positioned adjacent to one side of the stack, a first set of type faces coupled to said first rotatable support member, a second rotatable support member positioned adjacent to the other side of the stack, a second set of type faces each a mirror image of a type face of said first set coupled to said second rotatable support member, first drive means coupled to said first and second rotatable support members to drive said type faces sequentially past a print position on said stack, and second drive means to rapidly propel a type face and its mirror image type face together and apart relative to each other to compress said stack between said type faces for a brief interval of time to print a character on each sheet on the fly with a minimum of character divergence.

2. A device for printing a character on a plurality of sheets of paper interleaved with pressure sensitive marking means to form a stack comprising a first rotatable support member positioned adjacent to one side of the stack, a first set of type faces coupled to said first rotatable support member, a second rotatable support member positioned adjacent to the other side of the stack, a second set of type faces each a mirror image of a type face of said first set coupled to said second rotatable support member, synchronizing means coupled to said first and second rotatable members to position simultaneously a type face and its mirror image type face adjacent to opposite sides of said stack, and drive means to propel a type face and its mirror image type face together relative to each other to compress said stack between said type faces to print a character on each sheet with a minimum of character divergence.

3. A device for printing a character on a plurality of sheets of paper interleaved with pressure sensitive marking means to form a stack comprising a first rotatable support member positioned adjacent to one side of the stack, a first set of type faces coupled to said first rotatable support member, a second rotatable support member positioned adjacent to the other side of the stack, a second set of type faces each a mirror image of a type face of said first set coupled to said second rotatable support member, synchronizing means coupled to said first and second rotatable members to position simultaneously a type face and its mirror image type face adjacent to opposite sides of said stack, first drive means coupled to Said first and second rotatable support members to drive said type faces sequentially past a print position on said stack, and second drive means to rapidly propel a type face and its mirror image type face together and apart relative to each other to compress said stack between said type faces for a brief interval of time to print a character on each sheet on the fly with a minimum of character divergence.

4. A device for printing a character on a plurality of sheets of paper interleaved with pressure sensitive marking means to form a stack comprising a first rotatable support member positioned adjacent to one side of the stack, a first set of type faces coupled to said first rotatable support' member, a second rotatable support member positioned adjacent to the other side of the stack, a second set of type faces each a mirror image of a type face of said first set coupled to said second rotatable support member, indexing means coupled to indicate the presence of desired mirror image type faces in the print position, and drive means to propel a type face and its mirror image type face together relative to each other to compress said stack between said type faces to print a character on each sheet with a minimum of character divergence.

5. A device for printing a character on a plurality of sheets of paper interleaved with pressure sensitive marking means to form a stack comprising a first rotatable support member positioned adjacent to one side of the stack, a first set of type faces coupled to said first rotatable support member, a second rotatable support member positioned adjacent to the other side of the stack, a second set of type faces each a mirror image of a type face of said first set coupled to said second rotatable support member, indexing means coupled to indicate the presence of desired mirror image type faces in the print position, first drive means coupled to said first and second rotatable support members to drive said type faces sequentially past a print position on said stack, and second drive means to rapidly propel a type face and its mirror image type face together and apart relative to each other to compress said stack between said type faces for a brief interval of time to print a character on each sheet on the fiy with a minimum of character divergence.

6. A device for printing a character on a plurality of sheets of paper interleaved with pressure sensitive marking means to form a stack comprising a first rotatable support member positioned adjacent to one side of the stack, a first set of type faces coupled to said first rotatable support member, a second rotatable support member positioned adjacent to the other side of the stack, a second set of type faces each a mirror image of a type face of said first set coupled to said second rotatable support member, synchronizing means coupled to said first and second rotatable members to position simultaneously a type face and its mirror image type face adjacent to opposite sides of said stack, indexing means coupled to indicate the presence of desired mirror image type faces in the print position, and drive means to propel a type face and its mirror image type face together relative to each other to compress said stack between said type faces to print a character on each sheet with a minimum of character divergence.

7. A device for printing a character on a plurality of sheets of paper interleaved with pressure sensitive marking means to form a stack comprising a first rotatable support member positioned adjacent to one side of the stack, a first set of type faces coupled to said first rotatable support member, a second rotatable support member positioned adjacent to the other side of the stack, a second set of type faces each a mirror image of a type face of said first set coupled to said second rotatable support member, synchronizing means coupled to said first and second rotatable members to position simultaneously a type face and its mirror image type face adjacent to opposite sides of said stack, indexing means coupled to indicate the presence of desired mirror image type faces in the print position, first drive means coupled to said first and second rotatable support members to drive said type faces sequentially past a print position on said stack, and second drive means to rapidly propel a type face and its mirror image type face together and apart relative to each other to compress said stack between said type faces for a brief interval of time to print a character on each sheet on the fly with a minimum of character divergence.

8. A device for printing a character on a plurality of sheets of paper interleaved with pressure sensitive mark ing means to form a stack comprising a first rotatable support member positioned adjacent to'one side of the stack, a first set of type faces coupled to said first rotatable support member, asecond rotatable support member positioned adjacent to the other side of the stack, a second set of type faces each a mirror image of a type face of said first set coupled to said second rotatable support member, synchronizing means coupled to said first and second rotatable members to position simultaneously a type face and its mirror image type face adjacent to opposite sides of said stack, indexing means coupled to indicate the presence of desired mirror image type faces in the print position, first driving means coupled to said first and second rotatable support members to drive a desired type face towards its mirror image type face to compress said stack between said type faces to print a character on each sheet with a minimum of character divergence, second driving means coupled to withdraw said type faces from said stack after the printing process, and stepping means coupled to advance said stack to a new print position.

9. A device for printing a character on a plurality of sheets of paper interleaved with pressure sensitive marking means to form a stack comprising a first rotatable support member positioned adjacent to one side of the stack, a first set of type faces coupled to said first rotatable support member, a second rotatable support member, a second set of type faces each a mirror image of a type face of said first set coupled to said second rotatable support member positioned adjacent to the other side of the stack, synchronizing means coupled to said first and second rotatable members to position simultaneously a type face and its mirror image type face adjacent to opposite sides of said stack, first driving means coupled to said first and second rotatable support members to drive said type faces sequentially past a print position on said stack, indexing means coupled to indicate the presence of desired mirror image type faces in the print position, second driving means to rapidly propel a desired moving type face towards and away from its mirror image type face to briefly compress said stack between said type faces to print a character on each sheet on the fly with a minimum of character divergence, and stepping means coupled to advance said stack to a new print position.

10. A device for printing a character on a plurality of sheets of paper interleaved with pressure sensitive marking means to form a stack comprising a first rotatable support member positioned adjacent to one side of the stack, a first set of type faces coupled to said first rotatable support member, a second rotatable support member positioned adjacent to the other side of the stack, a second set of type faces each a mirror image of a type face of said first set coupled to said second rotatable support member, gears interposed between said first and second rotatable members to position simultaneously a type face and its mirror image type face adjacent to opposite sides of said stack, a driver gear coupled to said gears to drive said type faces sequentially past a print position on said stack, a pulse generator coupled to indicate the presence of mirror image type faces in the print position, a gate fed by said pulse generator to pass a signal to indicate the presence of desired mirror image type faces in the print position, forward driving means, magnetic means fed by said gate to couple said forward driving means to said support members to rapidly propel the desired moving type faces towards each other to briefly compress said stack to print simultaneously a character on each sheet on the fly with a minimum of character divergence, return driving means coupled to propel the desired moving type faces away from each other, and stepping means coupled to advance said stack to a new print position.

11. A device for printing a character on aplurality of sheets of paper interleaved with pressure sensitive marking means to form a stack comprising a first rotatable support member positioned adjacent to one side of the stack, a first set of type faces coupled to said first rotatable support member, a second rotatable support member positioned adjacent to the other side of the stack, a sec ond set of type faces each a mirror image of a type face of said first set coupled to said second rotatable support member, gears interposed between said first and second rotatable members to position simultaneously a type face and its mirror image type face adjacent to opposite sides of said stack, a driver gear coupled to said gears to drive said type faces sequentially past a print position on said. stack, a pulse generator coupled to indicate the presence of mirror image type faces in the print position, a gate: fed by said pulse generator to pass a signal to indicate the presence of desired mirror image type faces in the print position, a first fluted drive, magnetic means ener-- gized by said gate to couple said first fluted drive to said support members to propel rapidly the desired moving. type faces towards each other to print simultaneously a character on each sheet on the fiy with a minimum of character divergence, a second fluted drive coupled to propel the desired moving type faces away from each other, and stepping means coupled to advance said stack to a new print position.

12. A device for printing a character on a plurality of sheets of paper interleaved with pressure sensitive marking means to form a stack comprising a first rotatable support member positioned adjacent to one side of the stack, a first set of type faces coupled to said first rotatable support member, a second rotatable support member positioned adjacent to the other side of the stack, a second set of type faces each a mirror image of a type face of said first set coupled to said second rotatable support member, a gear train interposed between said first and second rotatable members to position simultaneously a type face and its mirror image type face adjacent to opposite sides of said stack, first drive means coupled to said gear train to drive said type faces sequentially past a print position on said stack, and second drive means to propel rapidly a type face and its mirror image type face together and apart relative to each other to compress said stack between said type faces for a brief interval of time to print a character on each sheet.

References Cited in the file of this patent UNITED STATES PATENTS 91,741 Hart June22, 1869 2,390,554 Plum Dec. 11,1945 

